Automotive ignitions have evolved through many iterations, and the field is well understood with much prior art.
The design eventually evolved to a standard jump spark “ignition coil” and “distributor” with “points”, by 1920. Later electronic switches were used. This remained the standard for almost 80 years: it is simple, reliable and cost effective. Systems that use other concepts, such as capacitor discharge, are not discussed here; they are not widely used.
As engine speeds rose, or more cylinders were added, an inherent problem or limitation of this design began to limit automotive performance. The standard ignition coil operates by building up a certain magnetic field, which takes some finite time, and the ignition coil stores energy in that field. The field is then suddenly collapsed, by the points opening (or equivalent), causing the spark. The spark may be 50-100 microseconds long (i.e., the collapse time). But the buildup time, set by the basic L/R (where L=inductance of coil; R=resistance) inherent time constant of the primary coil, is milliseconds long.
A small inductance implies less energy, so there is little to be gained in that direction in an attempt to shorten the storage time, without causing a smaller spark. The resistance can be increased, leading to so called “ballast resistors” in series with the coil, especially on 12-volt systems, by 1955. This approach wastes about half the energy as heat in the resistor, but improves the L/R time constant, allowing higher RPM without compromise of spark intensity. The field will build faster, but the maximum current is reduced, reducing the spark energy which is given by ½ LI2, where L=inductance and I=current. Many compromises result from this, with little real gain.
These same concerns are why V12 or V16 engines of the 30's and 40's typically had two distributors and two coils. This allows each coil to build up longer, as if it were on a 6-cylinder engine. Yet the coil is on a V12. However, that approach doubles the ignition system cost and complexity.
There were also attempts in the 40's and 50's in the racing field to operate two coils through one special V8 distributor cap with two sets of points opening alternately. This system, called “DUCOIL”, required a special distributor of difficult design with two rotors and two high voltage inputs. While the DUCOIL functioned well, it had little commercial success due to complexity, and it required two timing settings.
Finally, with computer control inherent in engines from the 90's forward, there has been a trend to use four or eight coils (i.e., “coil on plug”). That operates flawlessly, as there is plenty of time to build up the magnetic field with only one spark per revolution (or every other revolution) versus four or eight sparks per revolution on a V8 with one coil.
But this coil on plug is very expensive, as it requires not only four or eight coils but also the same number of associated high speed solid state power switches. It may draw a lot more electrical power, unless elaborately controlled buildup “on” time or duty cycle control is added. Such a controlled “on” time will be a function of engine RPM at least.
However, coil on plug is the standard approach today, despite the cost, as a single ignition on a V8 coil has proven marginal given emission issues.
There have been several patented designs using diodes in the high voltage leads of an ignition coil. For example, in U.S. Pat. No. 6,666,196 to Skinner (“Skinner”) the diodes are arranged not to direct the main spark, but to prevent an unwanted misfire or weak spark that can happen when the coil is first energized (called a “make spark” due to origins in point ignition). These diodes are described by Skinner as “less than 10 kV rated”, indicating no attempt to steer or hold off a 50 kV main spark; rather they conduct the main spark as if they were not there, but delete an inverse or “make spark”.
U.S. Pat. No. 5,586,542 to Taroya discloses an alternative method to suppress the make spark. U.S. Pat. No. 5,675,072 to Yasuda discloses a way to monitor the spark event status via a “sampling” diode, again without a spark directing function. U.S. Pat. No. 6,082,344 to Ito also discloses a method to suppress the make spark, this time by Zener diodes.
In U.S. Pat. No. 6,116,226 to Vogel, a high voltage switch (e.g., a Silicon Controlled Rectifier) is used to suppress the make spark, and to shorten the spark duration as the current tails off.
Applicant's present invention has no active switches in the high voltage; the above-listed U.S. Pat. No. 6,186,130 to Skinner has a similar goal (i.e., measuring spark current to determine an early cutoff point) but cuts off the primary current to allow beginning the building up sooner, for the next spark. This Skinner patent is an attempt to solve the same problem Applicant's two coil concept addresses successfully—the problem of the L/R time constant, by starting buildup as soon as possible. However, in Skinner, the L/R problem is still present with the one coil, even with elaborate electronic microprocessor control; it cannot be fully overcome.
U.S. Pat. No. 6,539,930 to Inagaki is also concerned with make spark suppression, combined with event monitoring and does not use two coils.
U.S. Pat. No. 6,405,708 to Watson discloses a method to fire one coil or ignition transformer, per cylinder; this single coil has dual outputs to fire two spark plugs at once; it is still a single core transformer, and such a coil, still with the L/R buildup problem, is well known from, e.g., motorcycles. But with typically fewer cylinders L/R is not a problem. U.S. Pat. No. 6,834,640 to Nishizawa also describes one coil per cylinder, and control means active to sense misoperation of the ignition event. Finally, U.S. Pat. No. 4,059,084 to Junot discloses adding a primary higher voltage to the ignition coil from a second low voltage energy storage coil. This is also an attempt to solve the L/R time constant problem, but Junot still describes a single high voltage ignition coil and no high voltage diodes.
In summation, although high voltage diodes are at times present, in the prior art, the purpose is either “make spark” suppression or monitoring the spark event.
Combining the interleaved alternating output, of the two or more independent coils using “OR” diodes into one HT (“high tension”) output lead, with a control to alternate the coil operation apparently has not been described.
Accordingly, it is a primary object of the present invention to provide an improved automotive ignition which overcomes the aforementioned problems in the prior art.
It is another primary object to provide a dual coil ignition system, commensurate with the above-listed object, which overcomes the prior L/R problem by alternately firing the coils.
It is a more specific object to provide a dual coil ignition system which combines the interleaved alternating output, of the independent coils using “OR” diodes into one HT output lead, with a control to alternate the coil operation.